Black smoke or blueish white smoke? Black smoke - it may just be excess fuel at start-up. Common with these engines from what I hear. Is it fumes from running rich that you smell? Kinda burns the nose and stings the eyes? May just be a carb adjustment. Bluish-white smoke is oil. How much oil does it use? If it consumes a lot and it's not accounted for from leaks(which should be fixed) , then I would say it's time for a rebuild.